Vacuum-tube circuits



Jan. 3, 192a. 1,654,945

D. C. PRINCE VACUUM TUBE CIRCUITS or iginal Filed Nov. 9, 1922 Pg. I.

Inventor David Cprince, YflQW K) 3 His Attorney Patented Jan. 3, 1928. I

UNITED STATES PATENT OFFICE.

DAVID C. PRINCE, OF SCHENECTADY, NEW YORK, ASSIGNOR T GENERAL ELECTRICCOMIANY, A CORPORATION OF NEW YORK.

VACUUM-TUBE CIRCUITS.

Application filed November 9, 1922, Serial No. 599,919. Renewed October27, 1927.

My present invention relates to vacuum tube circuits, and moreparticularly to cir- L cuits employed with vacuum tubes for producingalternating currents from direct currents. I

It has been recognized that for eiiiclent operation of a thermionicvacuum tube device as a rectifier, the tube losses should be made assmall as possible and that this result may best be accomplished by soarranging the circuit that a nearly constant current will flow for aconsiderable traction of a cycle, the current rising quickly from zeroto that value, then remalning constant and quickly falling to zeroagain.

is the product of current by the voltage drop across the tube at anyinstant will then be a minimum.

* 1nemployin thermionic vacuum tubes 29 for converting 'rect current toalternating, however, it has not been possible to obtain such higheiiiciency because of the fact that the voltage drop across the tube hasbeen sinusoidal and hence the potential drop has been a minimum at onlyone instant during the cycle. At all other instants it has been hi herand additional losses have resulted.

he object of my present invention is to provide circuit arrangementswhereby the difficultymentioned may be largely avoided and the princi a1losses will be those due to space charge, ament excitation and control,and these losses may be reduced to the minimum necessary tomake the tubeconduct current for the necessary fraction of a cycle. v

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims.

My invention itself, however, both as to its organization and method ofoperation will best be understood by reference to the followingdescription taken inconnection with the accompanying drawings in whichFigs. 1 to 3 inclusive, show diagrammatically as many difl'erent circuitarrangements whereby my invention may be carried into effect.

In the arrangement shown in Fig. 1, two three-electrode vacuum tubes 1and 2 are indicated. The plate circuits of these tubes include condenser3 and inductance 4, energy being supplied for the operation of the platecircuits from a direct current source 6 connected to the mid point ofinductance 4,

The tube loss whichthrough an inductance 5 which maintains the currentsupplied to the tubes substantially constant. The grid or controlcircuits of the tubes include an inductance 7, A common portion of thetwo grid circuits contains an inductance 9 and a resistance 10. Thecircuit to which alternating current is to be supplied may be connectedto inductance 8, which is coupled to inductance 4.-

Control excitation for the grids of the tubes is obtained from aseparate oscillating vacuum tube 12. The plate of tube 12 is connectedthrough inductance 13 with the direct current source 6. ihe grid circuitcontains an inductance 14, which is coupled to inductance 13, and theusual grid condenser 15 and grid leak 16. Inductances 13 and 14 are bothcoupled to inductance 7 which with condenser 11 is the frequencydetermining element of the separate source.

In the circuit arrangement shown in Fig. 2 self excitation of the tubes1 and 2 is obtained by means of the two inductance coils 17 and 18 whichare included in the grid circuits. Both of these coils are coupled toinductances 4, and coil 18 has a parallel condenser 19. Inductance 18and condenser 19 are proportioned to resonate at the same frequency asinductance 4 and condenser 3. The drops across inductances 17 and 18are, therefore in quadrature.

In Fig. 3 I have shown a circuit organization similar to thosedescribed, but arranged to produce three-phase current. In this case,three tubes 22, 23 and 24 are employed, The plates of these tubes areconnected' through inductances 27, 28 and 29 to choke inductance 25through which energy is fed from the direct current source 26.Inductances 30,31, 32 are inductively related to 27, 28 and 29respectively. These inductances are connected in delta and supply enerto a load such, for example, as a sync ronous motor 44, which is alsothe frequenc determining element. Inductances 2 28, 29, 30, 31 and 32may be iron cored transformers where the frequency is relatively low.Grid excitation is supplied from an assemblage of inductances 33, 34, 35and 36, 37, 38 arranged similarly to 27 to 32 inclusive. The individualgrids are fed through ballast resistances 41, 42, 43.

The neutral points of inductances 36, 37 and plate excitation 180 interminal through resistance 40 and inductance 39. Inductances 33, 34 and35 are fed from 30, 31, 32 in such a way. that the phase of the gridcontrol potentials can be varied.

To understand the operation of these circuits consider the operation ofFig. 1 as a rectifier, that is with the grids and their connectionsremoved. The impressed voltage is sinusoidal. This voltage iscommunicated by inductance 8 to inductance 4 and by it to the plates.The output is delivered to the generator 6, which now acts as an energyabsorbing device through inductance 5, which maintains the currentconstant. Now at constant current the drops across both tubes and energyabsorbing device are constant, therefore the difference between thesinusoidal impressed voltage and the c0nstant delivery voltage appearsas drop across the inductance 5- and does not occasion loss To secureanalogous operation it is necessary to observe that while the rid ispositive a rough proportionality exists between glrl'id and platecurrents. The grids are t erefore connected in a manner preciselysimilar to the plates being excited by inductance 7 and deliveringrectified current to load resistance 10 through inductance 9, whichmaintains the current constant. The grid and plate circuits are nowcooperating to deliver constant direct current from sinusoidalalternating current with minimum loss. To reverse the direction ofenergy flow it is only necessary to reverse the base and raise andreverse the potential of generator 6. Induct-ance 8 then automaticallybecomes an output instead of an input circuit. The losses have not beenchanged by this maneuver because during the portions of the cycle whencurrent flows the conditions have not been changed while a cessation ofgrid current in one tube indicates that the grid has become negativewith respect to the filament so that the plate current is cut off. Withthe arrangement shown in Fig. 2, then, current flows from each grid andeach plate substantially half the time, and during that 0' half the tubedrops are held constant by the 5 inductances 9 and 5 respectively. Thisgives the maximum output per tube and maximum efficiency obtainable witha given design of tube. During the period when current must betransferred from tube 1 to tube 2 there is a rapid change of current inthe circuit. In the plate circuit this rapid chan e can take place incondenser 3 where it wi set up no great voltage. At higher frequenciesthe condenser 11 of Fig. 1 provides a similar path for rapidly changinggrid currents. When the frequency is high even the inductance of leadsbegins to cause the current transfer in the grid circuit to lag behindthe voltage. It is necessary to compensate for this lag and for thecorresponding lag in the plate circuit. With a separate source of gridexcitation as shown in Fig. 1, and proper adjustment of the resonantcircuits the phases will automatically take up their proper relativepositions.

Fig. 2 shows an alternative method of securing phase angle correction.The grid excitation inductance has been divided into two sections 17 and18. Inductance 18 is tuned by condenser 19. Thevoltage induced in eachof these inductances by the current in inductance 4 is in quadraturewith the current. Since inductance 18 and condenser 19 tune they acttogether like a noninductive resistance. The current in this circuit istherefore in phase with the voltage and in quadrature with the currentin inductance 4. The self induced voltage in inductance 18 is inquadrature with the current in it and therefore the induced voltage ininductance 17 and the self-induced voltage in inductance 18 are inquadrature and an desired phase angle can be obtained by their propercombination.

Fig. 3 is based on the same principles as the preceding figures exceptthat instead of the current flowing at any one time in one of two tubesit flows in one of three. The resultant output is therefore three-phase.With polyphase out ut any desired phase angle can be secure forexcitation. This is done by the variable taps by which inductances 33,34 and 35 are excited from 30, 31 and 32. Additional grid resistances41, 42 and 43 may be found advantageous in some instances to acceleratethe current transfer from one grid to the succeeding. The maintenance ofsymmetrical threephaserelationships is dependent upon balance in theelement which determines the frequency and load.

Where it is important to minimize harmonics in the alternating currentcircuits two or more sets of single or three phase circuits may beassociated with the same primary inductances 30 to 35, inclusive. Inthis way any undesirable harmonics can be eliminated.

Certain features of the present application are disclosed and claimed inmy'copending application Serial No. 636,696, filed May 4, 1923, andassigned to the same assignee as the present application.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. A system for generating oscillations comprising a plurality ofelectron discharge devices having plate and grid circuits, a source ofdirect current for exciting the plate circuits, means for maintaininsubstantially constant the current supplied fiy said source, means forimpressing an alternating current upon the grid circuits, means formaintaining substantially constant the flow of current to the gridcircuits, and means for permitting of the ready transfer of the excitingcurrent from the grid circuitof one device to the grid circuit ofanother device.

2. A system for generating oscillations comprising a plurality ofelectron discharge devices having plate and grid circuits, a source ofdirect current for exciting the plate circuits, means for maintainingsubstantially constant the current supplied by said source,

. source of directcurrent means for impressing an alternating currentupon the grid circuits, means for varying the excitation of thedifferent grids to cause current to flow in the different plate circuitsat different intervals, means foi' maintaining substantially constantthe flow of current to the grid circuits, and means for permitting theready transfer current from the grid circuit of one device to the gridcircuit of another device.

3. A system for generating oscillations comprising a plurality ofelectron discharge devices having plate and grid circuits, a forexciting the plate circuits, means for maintaining substantiallyconstant the current supplied by said source, means for impressing analternating current upon the grid circuits, an inductance of suitablevalue which is common to all of the grid circuits for maintainingsubstantially constant the flow of current'to the grid circuits, andmeans for permitting of the ready transfer of the exciting current fromthe grid circuit of one device to the grid circuit of another device.

4. A system for generating oscillations comprising a plurality ofelectron discharge devices having plate and grid circuits, a source ofdirect current for exciting the plate circuits, means for maintainingsubstantially constant said source, means for impressing an alternatingcurrent upon the grid circuits, means for varying the excitation of thedifferent grids to cause current to flow in the different plate circuitsat different intervals, means for permitting of the readv transfer ofthe exciting current from the grid circuit of one device to the gridcircuit of another device, and an inductance of suitable value which iscommon to all of the grid circuits for maintaining substantiallyconstant the flow of current to the grid circuits.

, 5. A system for generating oscillations comprising a plurality ofelectron discharge devices having plate and grid circuits, a

source of direct current for exciting the plate circuits, means formaintaining substantially constant the current supplied by said source,means for im ressing an alternating current upon the gri circuits, meansfor adjusting the phase of the currents supplied to the grid circuits,and means for maintaining substantially constant the flow of current tothe grid circuits.

of the exciting the current supplied by 6. A system for generatingoscillations comprising a plurality of electron discharge devices havingplate and grid circuits, a source of direct current for exciting theplate circuits, means for maintaining substantially constant the currentsupplied by said source, means for impressing an alternating currentupon the grid circuits, means for varying the excitation of thedifferent grids to cause current to flow in the different plate circuitsat different intervals, means for adjusting the phase of the currentssupplied to the grid circuits, and means for maintaining substantiallyconstant-the efiow of current to the grid circuits.

' 7 A system for generating oscillations comprising a plurality ofelectron discharge devices having plate and grid circuits, a source ofdirect current for exciting the plate circuits, means for maintainingsubstantially constant the current supplied by said source, means forimpressing an alternating current upon the grid eircuits, an inductanceof suitable value which is common to all of the grid circuits formaintaining substantially con stant the flow'of current to the gridcircuits and means for adjusting the phase of the currents supplied tothe grid circuits.

8. A system for generating oscillations comprising a plurality ofelectron discharge devices having plate and grid circuits, a

source of direct current for exciting the plate circuits, means formaintaining substantially constant the current supplied by said source,means for impressing an alternating current upon the grid circuits,means for adjusting the phase of the current supplied to the gridcircuits means for varying the excitation of the different grids tocause current to flow in the different plate circuits at differentintervals, and an inductance of suitable Value which is common to all ofthe grid circuits for maintaining substantially constant the flow ofcurrent to the grid circuits.

9. The combination in a system for producing polyphase alternatingcurrent from direct current of a plurality of electron discharge deviceshaving plate and grid circuits, a source of direct current for excitingthe plate circuits, inductances in the plate circuits which form theprimarywindings of a polyphase transformer, inductances in the gridcircuits which form the secondary windings of a second polyphasetransformer and adjustable taps connected to the secondary windingprimary windings of the second transformer whereby polyphase currents ofa desired phase may be supplied to the primary Winding of the secondtransformer.

In witness whereof. I have hereunto set my hand this 8th day ofNovember, 1922.

AVID c. PRINCE.

of the first transformer from the

